1. Field of the Invention
The present invention relates to a target searching method of and a target searching apparatus for providing a user, who is on a movable body moving on a route to a destination set in advance, with positional information related to a reach target on or near the set route to be reached by the movable body.
2. Description of the Related Art
There is a so-called navigation apparatus, which displays a map including a position where a movable body in various kinds such as an automobile, an airplane, a ship etc., is currently located, and further superimposes a position mark indicating a position of the movable body at the currently located position on the displayed map, so as to perform a route guidance or navigation to the destination on the basis of the display. Among the navigation apparatuses, as on-vehicle navigation apparatuses which are mounted on vehicles or auto-mobiles, there is a self-sustained or built-in type navigation apparatus and a GPS (Global Positioning System) type navigation apparatus as rough categories.
The former is a navigation apparatus, which obtains a moving direction and a moving distance of the movable body by use of a speed sensor, an angular speed sensor etc. equipped in or built in the pertinent vehicle, adds them with respect to a standard position so as to calculate the present position, and displays the present position mark and the corresponding map on the display picture plane on the basis of the calculated present position.
On the other hand, the latter is a navigation apparatus, which receives electric waves from a plurality of GPS satellites launched in the space, calculates the present position of the movable body by means of a 3-dimensional measuring method or a 2-dimensional measuring method on the basis of the electric wave reception results, and displays the present position mark and the corresponding map on the display picture plane on the basis of the calculated present position.
Further, there is an on-vehicle navigation apparatus provided with both functions of the above described self-sustained type and GPS type.
According to the above explained navigation apparatus, since the user (e.g. the driver) can grasp the present position of the self vehicle and the map in the vicinity of the present position in association with each other, it is possible to reach a destination without losing his or her way even in an area where the user has never experienced.
Further, the on-vehicle navigation apparatus may have a so-called target searching function. Namely, as the user designates a type or attribute of reach target such as a gasoline station or the like to be reached, the position or positions corresponding to the reach target of the designated type or attribute, which is or are positioned within a predetermined region [e.g., a region which is directed within right and left 45 degrees (90 degrees in total) with respect to the advance direction of the self vehicle at the center thereof and which distance from the self vehicle is within 10 km], is or are superimposed on the map to be displayed.
However, in the above explained target searching function, since the size of the predetermined region and the positional relationship between the predetermined region and the self vehicle are fixed, it may happen a case where an appropriate reach target in line with a moving condition of the self vehicle cannot be searched and displayed depending on the moving condition, which is a problem.
Namely, it is assumed such a case that the self vehicle is executing the above mentioned target searching function while traveling on a highway road, for example. In this case, although it is not possible for the self vehicle to exit from the highway road unless traveling via the interchange, the reach target is displayed which is within the above mentioned predetermined region but cannot be actually reached since it is not on the highway road and since the interchange is not located at the vicinity of the self vehicle, which is the problem.
Further, even while moving on an ordinary road (i.e. a road other than the highway road), it may happen a case that the reach target located on a route, which is too narrow for the vehicle to pass therethrough, is displayed, which is another problem.